Observation of the Semileptonic Decays B --> D* tau nubar and Evidence for B --> D tau nubar

TL;DR

This paper reports measurements of semileptonic B meson decays involving tau leptons, providing data that could reveal physics beyond the Standard Model, based on a large dataset collected with the BaBar detector.

Contribution

First measurement of B --> D(*) tau nu decays using BaBar data, offering insights into potential new physics effects in semileptonic B decays.

Findings

Branching fraction B(B --> D tau nu) = (0.86 +/- 0.24 +/- 0.11 +/- 0.06)%

Branching fraction B(B --> D* tau nu) = (1.62 +/- 0.31 +/- 0.10 +/- 0.05)%

Evidence supporting potential deviations from Standard Model predictions

Abstract

We present measurements of the semileptonic decays B- --> D0 tau- nubar, B- --> D*0 tau- nubar, B0bar --> D+ tau- nubar, and B0bar --> D*+ tau- nubar, which are potentially sensitive to non--Standard Model amplitudes. The data sample comprises 232x10^6 Upsilon(4S) --> BBbar decays collected with the BaBar detector. From a combined fit to B- and B0bar channels, we obtain the branching fractions B(B --> D tau- nubar) = (0.86 +/- 0.24 +/- 0.11 +/- 0.06)% and B(B --> D* tau- nubar) = (1.62 +/- 0.31 +/- 0.10 +/- 0.05)% (normalized for the B0bar), where the uncertainties are statistical, systematic, and normalization-mode-related.